1. Field of the Invention
The present invention relates to a tester for testing acceptability of an electronic device. More particularly, the present invention relates to a tester for testing the acceptability of the electronic device based on quantity of jitter of an output signal output from the electronic device.
2. Description of Related Art
Conventionally, in order to calculate quantity of jitter of an output signal output from an electronic device, the output signal output from the electronic device is measured multiple times by an oscilloscope or the like and the quantity of jitter is calculated from wave form of the measured output signal. For example, timing of the output signal consisting with a predetermined reference value is measured, and the quantity of jitter of rising and falling of the output signal are calculated by variation of the timing.
In recent years, jitter of an output signal output from a semiconductor element of an electronic equipment has been a problem with complication of the electronic equipment. For this reason, improvement in the analysis of the quantity of jitter for each path of the semiconductor device and calculation accuracy of the quantity of jitter etc. is desired. However, it has been difficult to calculate the quantity of jitter with sufficient accuracy by the conventional calculation methods of the quantity of jitter due to an error in function of the oscilloscope or the like. Moreover, since it is necessary to operate the oscilloscope etc. manually, it takes a lot of time to calculate the quantity of jitter.
In order to solve the aforesaid problem, according to the first aspect of the present invention, there is provided a jitter quantity calculator for calculating quantity of jitter of an output signal output from an electronic device. The jitter quantity calculator includes: a timing generator for generating timing; a value calculating section for calculating a value of the output signal multiple times based on the timing generated by the timing generator; a first decision section for deciding whether the value of the output signal, which is calculated by the value calculating section multiple times, is greater than or equal to a first reference value, and for outputting the decision result; a second decision section for deciding whether the value of the output signal, which is calculated by the value calculating section multiple times, is greater than or equal to a second reference value, and for outputting the decision result; and a jitter calculating section including first calculation means for calculating the quantity of jitter of the output signal based on the number of times the value of the decision result of the output signal is less than the first reference value in the first decision section and the value of the output signal is greater than or equal to the second reference value in the second decision section. The timing generator generates different timing whenever the value calculating section calculates the value of the output signal a predetermined number of times, and the first calculation means calculates the quantity of jitter of the output signal based on the number of the decision for each of the different timings.
According to the first aspect of the present invention, the jitter calculation section may further include second calculation means for calculating the quantity of jitter of the output signal based on the number of times the value of the decision result of the output signal is greater than or equal to the first reference value in the first decision section. The second calculation means may calculate the quantity of jitter of the output signal based on the number of the decision for each of the different timings. The jitter calculation section may further include third calculation means for calculating the quantity of jitter of the output signal based on the number of times the value of the decision result of the output signal is less than the second reference value in the second decision section. The third calculation means may calculate the quantity of jitter of the output signal based on the number of the decision for each of the different timings. The jitter calculation section may further include third calculation means for calculating the quantity of jitter of the output signal based on the number of times the value of the decision result of the output signal is less than the second reference value in the second decision section. The third calculation means may calculate the quantity of jitter of the output signal based on the number of the decision for each of the different timings, and the jitter quantity calculator may further include a calculation means selection section for selecting either the first calculation means, the second calculation means or the third calculation means to causes it to calculate the quantity of jitter of the output signal.
Moreover, the timing generator may generate two timings in a predetermined interval, the first decision section may decide whether the value of the output signal, which is calculated multiple times by the value calculating section based on one of the two timings, is greater than or equal to the first reference value, and outputs the decision result, the second decision section may decide whether the value of the output signal, which is calculated multiple times by the value calculating section based on the other timing of the two timings, is greater than the second reference value, and outputs the decision result, and the timing generator may generate two different timings whenever the value calculating section calculates the value of the output signal a predetermined times.
The jitter calculation section may further include fourth calculation means for calculating the quantity of jitter of the output signal based on the number of times the value of the decision result of the output signal is greater than or equal to the first reference value in the first decision section and the value of the output signal is less than the second reference value in the second decision section. The fourth calculation means may calculate the quantity of jitter of the output signal based on the number of the decision for each of the two different timings. The jitter calculation section may further include fifth calculation means for calculating the quantity of jitter of the output signal based on the number of times the value of the decision result of the output signal is greater than or equal to the first reference value in the first decision section and the value of the output signal is greater than or equal to the second reference value in the second decision section. The fifth calculation means may calculate the quantity of jitter of the output signal based on the number of the decision for each of the two different timings. The jitter calculation section may further include sixth calculation means for calculating the quantity of jitter of the output signal based on the number of times the value of the decision result of the output signal is less than the first reference value in the first decision section and the value of the output signal is less than the second reference value in the second decision section. The sixth calculation means may calculate the quantity of jitter of the output signal based on the number of the decision for each of the two different timings.
Moreover, the jitter calculation section may further include: fifth calculation means for calculating the quantity of jitter of the output signal based on the number of times the value of the decision result of the output signal is greater than or equal to the first reference value in the first decision section and the value of the output signal is greater than or equal to the second reference value in the second decision section; and sixth calculation means for calculating the quantity of jitter of the output signal based on the number of times the value of the decision result of the output signal is less than the first reference value in the first decision section and the value of the output signal is less than the second reference value in the second decision section. The fifth calculation means and the sixth calculation means may calculate the quantity of jitter of the output signal based on the number of the decision for each of the two different timings, and the jitter quantity calculator may further include a calculation means selection section for selecting either the first calculation means, the fourth calculation means, the fifth calculation means or the sixth calculation means, and for causing it to calculate the quantity of jitter of the output signal. The jitter calculation section may further include a storage section for storing the number of the decision for each of the different timings which are generated by the timing generator whenever the value calculating section calculates the value of the output signal a predetermined number of times.
Moreover, the calculation means selection section may supply selection information to the jitter calculating section, the selection information indicating a either of the calculation means which is to be selected among the first calculation means, the fourth calculation means, the fifth calculation means or the sixth calculation means. The jitter calculating section may receive the selection information and the decision result of the first decision section and the second decision section. The jitter calculating section may decide whether each of the decision result satisfies criteria of the selected calculation means. The jitter calculating section may count the number of times the decision result satisfies the criteria, as the number of the decision.
Moreover, the calculation means selection section may supply a switching signal INV1 and a switching signal INV2, which indicate the criteria of the calculation means which is to be selected, to the quantity-of-jitter calculating section as the selection information. The jitter calculating section may include: a first criteria comparison section for receiving the switching signal INV1 and a decision result of the first decision section, and for deciding whether the decision result of the first decision section satisfies the criteria of the selected calculation means; a second criteria comparison section for receiving the switching signal INV2 and the decision result of the second decision section, and for deciding whether the decision result of the second decision section satisfies the criteria of the selected calculation means; a third criteria comparison section for deciding whether the decision result of both the first decision section and the second decision section satisfies the criteria of the selected calculation means based on the decision result of the first criteria comparison section and the second criteria comparison section; and a counter for counting the number of times both of the criteria of the selected calculation means are satisfied in the third criteria comparison section as the number of the decision.
Moreover, the first criteria comparison section may be a first exclusive-OR circuit outputting exclusive OR of the decision result of the first decision section and the switching signal INV1, the second criteria comparison section may be a second exclusive-OR circuit outputting exclusive OR of the decision result of the second decision section and the switching signal INV2, the third criteria comparison section may be an AND circuit outputting AND of negation of the output of the first exclusive-OR circuit, and negation of the output of the second exclusive-OR circuit.
Moreover, the first decision section may include a first switching section for switching whether to supply the decision result of the first decision section to the jitter calculating section, the second decision section may include a second switching section for switching whether to supply the decision result of the second decision section to the jitter calculating section, and the calculation means selection section may supply a control signal CPE for controlling the first switching section and the second switching section to the first switching section and the second switching section. Moreover, the jitter calculating section may further include a third switching section for switching whether to supply the decision result of the third criteria comparison section to the counter based on the control signal CPE.
According to the second aspect of the present invention, there is provided a tester for deciding acceptability of an electronic device. The tester includes: a signal generator for generating a test signal for test and for inputting it into the electronic device; a jitter quantity calculator for calculating quantity of jitter of an output signal output from the electronic device based on the input test signal; and an acceptability decision section for deciding the acceptability of the electronic device based on the quantity of jitter calculated by the jitter quantity calculator. The jitter quantity calculator includes: a timing generator for generating timing; a value calculating section for calculating a value of the output signal multiple times based on the timing generated by the timing generator; a first decision section for deciding whether the value of the output signal, which is calculated by the value calculating section multiple times, is greater than or equal to a first reference value, and for outputting the decision result; a second decision section for deciding whether the value of the output signal, which is calculated by the value calculating section multiple times, is greater than or equal to a second reference value, and for outputting the decision result; and a jitter calculating section including first calculation means for calculating the quantity of jitter of the output signal based on the number of times the value of the decision result of the output signal is not greater than or equal to the first reference value in the first decision section and the value of the output signal is greater than or equal to the second reference value in the second decision section. The timing generator generates different timing whenever the value calculating section calculates the value of the output signal a predetermined number of times, and the first calculation means calculates the quantity of jitter of the output signal based on the number of the decision for each of the different timings.
The summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the features described above.